CRC Project 1 Abstract Non-gonococcal urethritis (NGU) is the most common form of urethritis in men and cure rates are only 70- 80%, reflecting deficits in understanding of the syndrome. Known NGU etiologies include Chlamydia trachomatis, Mycoplasma genitalium, Trichomonas vaginalis, Ureaplasma urealyticum, and Herpes simplex virus but for 30-40% of NGU there is no clear causal agent. We propose to re-evaluate the origins of NGU through comprehensive microbiological evaluation of a cohort of heterosexual men with acute NGU and their regular sex partners comparing them to men without NGU and their partners. Evaluation of couples rather than individuals will provide novel insights into the transmission (i.e. concordance) of agents causing NGU, help define transmissibility of less well characterized organisms, and allow identification of factors within sexual partnerships that contribute to or help prevent NGU. Project 1 Specific Aims are: Aim 1: Determine concordance rates for known STIs in sexual partnerships for men with and without acute NGU. Hypothesis 1: Concordance will be higher for contributors to NGU pathogenesis among sexual dyads where men have NGU. Symptomatic NGU will be associated with higher concentrations of NGU-specific organisms, leading to higher concordance rates for partners. 1A. Determine the prevalence and infection concordance rates among sex partners for C. trachomatis, M. genitalium, T. vaginalis, U. urealyticum, G. vaginalis, and HSV. 1B. Compare the urethral microbiomes of men with and without NGU to microbiome composition from sex partners' sites of sexual exposure (genital, rectal or oral). Understanding within dyad similarities of pathogens and microbiome communities will inform future NGU and partner management strategies. Aim 2: To prospectively describe the effect of treatment on microbiome characteristics of persons with NGU and their partners. Hypothesis 2. Following therapy and unlike untreated persons, the microbiomes of men with NGU and their partners will change and inflammation will resolve. In men with pathogen negative NGU, microbiome composition will no longer reflect partners' microbiomes. Aim 3: Indentify microbiome characteristics that may protect against NGU. Hypothesis 3: Like lactobacili in the vagina, certain other bacteria help sustain a healthy urethral microbial environment. These beneficial bacteria will predominate in the healthy male urethra. We propose that U. parvum is protective in the male urethra. U. parvum will be found more frequently in men without NGU and their partners. Together these studies will improve understanding and management of acute NGU in men.